A bioreactor for such treatment of liquids is described in U.S. Pat. 4,654,308 issued Mar. 31, 1987 to Safi et al. This patent describes the need to treat liquids containing organic matter, such as in the pulp and paper industry or the cheese processing industry due to pollution regulations imposed by governments.
When a substrate, during anaerobic treatment, comes into contact with microorganisms, it is converted into gas by means of two principal reactions which occur in sequence.
The first reaction to occur, known as acidogenesis reaction, is when the substrate is converted to volatile acids due to the action of the acidogenesis microorganisms. In this reaction, the rate of conversion into acids of the substrate is proportional to the concentration of the substrate.
The second reaction, known as methanogenesis reaction, occurs when the volatile acids, through the action of methanogenesis micro-organisms, are converted into methane (biogas). In this reaction, the rate of conversion of the volatile acids into methane is inversely proportionate to the concentration of volatile acids.
In general, both described reactions occur sequentially in the same reactor.
The bioreactor defined in the above mentioned U.S. patent consists of a tubular container with a plurality of spaced apart trays, each tray being apertured to provide liquid flow communication between the inlet and outlet with apertures of alternate trays being arranged relative to one another to cause the liquid to flow laterally across the respective cell beds of the trays as the liquid flows from one tray to another. It has been found, however, that there is a possibility for the fluid and the microorganism cells to return to the lower compartment, thus greatly reducing the efficiency of the reactor.